Spring is here and so are the carpenter bees. Carpenter bees are very active from early spring through summer around houses and other wooden structures. These insects earn their name because they bore one-half inch wide holes that appear to be perfectly round on exterior wooden surfaces. They naturally nest in dead trees and woodpiles, but they also bore into exterior wood on buildings, fences, decks, and outdoor furniture. Homeowners are often frightened by these pesky black bees that fly erratically around their homes. The male carpenter bee is very territorial and protects its nesting sites, hovering nearby and attacking intruders. Although the male behaves aggressively, it does not have a stinger, making it harmless. The female has a stinger but is not defensive and rarely stings. Males have a white or yellow blaze on their face, while females have a dark face.
Homeowners often mistake carpenter bees with bumble bees because of their similarities in size and appearance. Actually, there are many species of bumble bees and carpenter bees, each with unique color patterns, but most carpenter and bumble bees are yellow and black. The quickest way to tell a carpenter bee from a bumble bee is by looking at its abdomen. Carpenter bees have few hairs on the abdomen, making them look “shiny,” while bumble bee abdomens are very hairy and “fuzzy” looking. It is important to distinguish between carpenter bees and bumble bees because they behave very differently. Carpenter bees are solitary bees that nest in excavated wooden tunnels. Bumble bees are social bees that develop colonies of dozens of sister bees that nest in the ground. Because carpenter bees are solitary bees, they are less defensive of their nest sites; whereas, bumble bees are extremely defensive when their nest site is disturbed.
Adult female and male carpenter bees overwinter in abandoned nest tunnels where they have stored small amounts of pollen. The adults emerge in early spring to mate and search for nest sites. Females may use old abandoned nest tunnels or excavate new galleries to lay her eggs. Each gallery (or tunnel) will hold six to eight cells. A female will mix pollen and nectar to form “bee bread,” lay an egg on the ball of bee bread and seal off each cell with chewed wood pulp. The egg hatches and the larva (grub stage) develops into the adult, which chews through the cell partition and emerges in late summer.
Carpenter bees are good pollinators and should not be harmed. Unfortunately, they also can be pests around homes, causing considerable structural damage when they repeatedly colonize exposed wood. An early sign of carpenter bee damage is coarse sawdust that collects beneath excavated cavities during the spring of the year. Unsightly stains caused by falling bee waste around the entrance hole may also develop. Homeowners often notice a buzzing or burrowing sound coming from within the wood. The excavating bee will bore directly into the wood with her mouth parts for about an inch, then turn sharply and bore at a 90-degree angle, usually along the grain of the wood. Normally, the gallery will extend about four to six inches, but with repeated use, galleries have measured ten feet long. Nest sites by a single bee result in slight damage, but repeated colonization over several years may result in considerable damage. In addition, the open holes allow water intrusion that also can create considerable moisture damage over time. Also, woodpeckers feeding on the developing bee larvae will tear into the galleries, further damaging the wood to the point where it needs replacing.
Unpainted, exposed wood is especially attractive to carpenter bees. The most effective deterrent to carpenter bee activities is a painted surface. Unfortunately, painting or placing polyurethane on wood decks or log homes is often not a desirable option. Wood stains provide little repelling action. If practical, remove severely damaged wood and it replace with chemical pressure-treated wood to deter nest construction. Synthetic surfaces such as vinyl or HardiePlank™ siding are not damaged by carpenter bees.
Sometimes it is necessary to control carpenter bees causing damage. There are several commercial and homemade traps where carpenters crawl in and cannot get out. While these traps will collect carpenter bees if properly installed, traps often do not provide total control around a structure, leaving other carpenter bees to continue to do damage.
The goal of treating for carpenter bees should be to deter the nesting damage but not eliminate all of the bees in the yard because they are important pollinators. For this reason, applications to nest sites are preferable to broadcast applications over the yard. There are insecticide dusts, aerosols, foaming aerosols and liquid sprays labeled for carpenter bee control and can be applied to exposed wood and gallery entrances. Many of these products will contain one or two pyrethroid insecticides such as bifenthrin, cypermethrin, cyhalothrin, permethrin, prallethrin, and tetramethrin. Sprays can be the easiest to apply, but a problem with many sprays is they get soaked into raw wood and are not available to kill the bees. Aerosol sprays, especially foaming formulations with a straw attachment, can be effective if applied to each hole, but the chemical can also get soaked into raw wood over time. Dusts applied to each hole will stay on the surface and can be effective, but dusts can be messy to apply without a small insecticide duster made for this type of application.
Whatever product is used, all label directions must be followed. Even if personal protective equipment is not required on the label, it is always a good idea to wear a long-sleeved shirt, chemically resistant gloves, and protective eyewear when making applications.
If you are concerned about being stung by the females, control efforts should be conducted in the evening or at night when the bees are resting inside the wood tunnels. After twenty-four hours post-treatment, all tunnel entrances should be plugged with a wooden dowel coated with wood glue or steel wool covered with caulk to prevent re-colonization by other nesting bees. You can use wood putty or caulking compound only, but if an insecticide is not used, the trapped adult carpenter bees can excavate new openings. It can be very difficult to reach many of the holes the bees are using. However, if holes are not treated and plugged, the carpenter bees will probably continue to reuse the same hole every year. Also, water incursion will likely occur, leading to wood rot.
If treatment just seems too difficult, you may want to hire a pest management professional. Most have the experience and equipment needed to make an effective and safe application.